This invention relates to derivative strains of a newly discovered microorganism Thermoanaerobacter ehtanolicus, a thermophilic anaerobe. More specifically, this invention relates to producing ethanol using derivatives of the microorganism Thermoanaerobacter ethanolicus.
The microorganism Thermoanaerobacter ethanolicus has been described as an extreme thermophilic, non-spore-forming anaerobic bacterium which ferments a variety of carbohydrates to ethanol as the main product (Wiegel, J. and Ljungdahl, L. G., Arch. Microbiol. 128, 343-348, 1981). Relatively few thermophilic anaerobic bacteria, which ferment substrates such as starch, cellobiose, glucose, xylose, and other sugars to ethanol as the main product, have been reported. The microorganism Thermoanaerobacter ethanolicus is described in U.S. Pat. No. 4,292,407 which is incorporated herein by reference. A related patent is U.S. Pat. No. 4,292,406 which is incorporated herein by reference.
The present invention overcomes problems of fermentations yielding low concentrations of ethanol using the microorganism Thermoanaerobacter ethanolicus.
The present invention produces ethanol at a substrate concentration in a fermentation medium greater than 1% (w/v) using biologically pure cultures of derivatives of the microorganism Thermoanaerobacter ethanolicus. The present invention provides derivatives having the ability to ferment substrates such as starch, cellobiose, glucose, xylose and other sugars to ethanol under anaerobic and thermophilic conditions in an aqueous, nutrient medium obtaining ethanol concentrations high enough to make continuous fermentations possible. Specifically, substrate can be added to a fermentation medium and ethanol can be removed therefrom during the same continuous fermentation.
The derivative strains, produced both through induced mutagenesis and multiple selections for spontaneous mutations (described in Examples I, II, and III below) differ from the parent strain, strain JW200 of the microorganism Thermoanaerobacter ethanolicus (ATCC 31550), in that the production of ethanol continues at a high rate although the ethanol concentration in the fermentation medium is greater than 1% (w/v) and substrate concentrations in the fermentation medium are greater than 1% (w/v). The following derivative strains are representatives of a large number of derivative strains obtained from the parent strain, strain JW200 of the microorganism Thermoanaerobacter ethanolicus (ATCC 31550). These biologically pure cultures of the representative derivative strains, specifically, strain JW200L-Large of the microorganism Thermoanaerobacter ethanolicus (ATCC 31936) representative of ultraviolet light mutagenesis and pyruvate selection; strain JW200Fe(3) of the microorganism Thermoanaerobacter ethanolicus (ATCC 31937) representative of iron deprivation selection and low growth on pyruvate; and strain JW200L-Fe(7) of the microorganism Thermoanaerobacter ethanolicus (ATCC 31938) representative of ultraviolet light mutagenesis, iron deprivation and low growth on pyruvate, are ethanol tolerant up to 10% (v/v) ethanol in the fermentation medium. The foregoing representative derivative strains produce ethanol at ethanol concentrations in a fermentation medium greater than 1% (w/v) whereas the parent strain does not produce ethanol at ethanol concentrations in a fermentation medium greater than 1% (w/v). The parent strain, strain JW200 of the microorganism Thermoanaerobacter ethanolicus (ATCC 31550), tolerates ethanol concentrations of up to 10% (v/v) ethanol in the fermentation medium only if given time to grow in low concentrations first. The above referenced derivative strains do not show this characteristic of the parent strain, strain JW200 of the microorganism Thermoanaerobacter ethanolicus (ATCC 31550).
It is an object of the present invention to produce ethanol at substrate concentrations in a fermentation medium above 1% (w/v) using biologically pure cultures of derivatives of the microorganism Thermoanaerobacter ethanolicus.
It is a further object to continuously produce recoverable amounts of ethanol from substrates such as starch, cellobiose, glucose, xylose, and other sugars.
These and other objects, aspects and advantages of this invention will become apparent from a consideration of the accompanying specification and claims.